1. Field of the Invention
The present invention relates to an auxiliary memory device for electronic devices and, particularly, to a small-sized detachable memory card suitably used for portable electronic devices such as digital cameras or others.
2. Description of the Related Art
Conventionally, as an auxiliary memory device used for portable electronic devices such as digital cameras or others, a small-sized memory card capable of being detachably mounted to the bodies of the electronic devices has been known in the art. This type of memory card, which may be referred to as a flash memory, is structured by assembling a card-shaped hollow casing generally made of resin or metal, a circuit board carrying electronic parts thereon and a connector for forming terminals on the circuit board, the circuit board and the connector being incorporated within the casing.
A typical conventional memory card (i.e., a flash memory) is diagrammatically illustrated in FIG. 9, and includes a card-shaped hollow casing 1 which is divided into two halves generally at a center of a card thickness. Each of the two halves 2 and 3 of the casing 1 has, on a surface 4 thereof confronting the surface 4 of the other half, a section for securely arranging a connector 5 and a section for receiving a circuit board 6 carrying electronic parts (not shown) on the major surface thereof. The two halves 2 and 3 are fixed to each other and the connector 5 and the circuit board 6 are accommodated therein. Each half 2, 3 also includes a rib 7 which is formed to project along an outer peripheral edge region of the surface 4. The end face of the rib 7 of one half 2 is firmly fixed to the end face of the rib 7 of the other half 3 by a well-known fixing means such as ultrasonic welding.
In general, the circuit board 6 is mechanically and stably supported in the casing 1 by the connection of conductor ends (not shown) of the circuit board with the connector 5. The conventional memory card includes such a laminated casing structure, and thus is provided with mechanical protection and electrical insulation properties for the electronic parts on the circuit board 6 as well as a desired level of rigidity of the entire structure of the memory card.
Recently, it has been required, for portable electronic devices, to have multiple functions and high performance, as well as to further reduce the size and weight of the body of the electronic devices. To satisfy such requirements, it has been also contemplated that the dimension of the memory card used as an auxiliary memory device is further reduced. Under such circumstances, the conventional memory card having a laminated casing structure may be deteriorated in the rigidity of the entire structure of the memory card due to the reduction of card size, particularly in the rigidity or durability against a destruction which may be caused, at the rib end faces fixed with each other, to the two halves of the card casing when the casing is twisted.
In order to prevent such a deterioration of rigidity, it is necessary to provide a sufficiently wide fixing area on the rib end face of each casing half, which may restrict the size reduction of the casing. That is, even if the circuit board is miniaturized to a minimum dimension while meeting the functional requirement thereof, the outside dimension of the casing (particularly, a two-dimensional size defined parallel to the major surface of the circuit board) tends to become considerably large, relative to the circuit board size, due to the wide fixing area of the rib end face of each casing half.